A scroll compressor has a predetermined internal volume ratio depending on the specifications of its scroll wraps. Where the operating condition yields a proper compression ratio for the internal volume ratio, no inappropriate compression loss will result. However, an inappropriate compression loss is caused under an operating condition that yields a lower compression ratio than the proper compression ratio. This is called an over-compression loss. Another inappropriate compression loss is caused under an operating condition in which the compression ratio is a higher than the compression ratio. This is called an insufficient compression loss. Usually, the effect of inappropriate compression loss is reduced by selecting a specification of scroll wrap such that the scroll wrap has an internal volume ratio tailored to an operating condition most prioritized in view of various conditions such as the rated condition and the operation frequency.
To suppress over-compression loss, reducing the flow path resistance in discharge pathways is effective. The discharge pathways refer to those in which gas is discharged after compression from the compression chamber (innermost chamber) in the scroll wrap center. To suppress insufficient compression loss, reducing a so-called the dead volume is effective. The dead volume is the volume of the innermost chamber on communicating with the second chamber when the compression is completed. The dead volume depends on the internal volume ratio. Some conventional techniques have minimized the volume of the innermost chamber while securing the strength of the center part of the scroll wrap to reduce insufficient compression loss (see, for example, Patent Literature 1).